1. Field of Invention
This invention relates to manufacturing process control and in particular, real time monitoring of process parameters and statistical process control.
2. Description of Related Art
High yield is maintained through a high level of process control which includes having the right process recipe, collecting process parameter data and comparing the data to a set of established control limits. Often this entails fine tuning of the process in an attempt to optimize the process to produce higher yield. Measurements of key process parameters needed to understand the status of a process has been manually collected and often without the continuity or history to produce the desired results. Attempts have been made to automatically collect and warehouse the parameter data. This can be difficult because of the volume of data. The development of statistical techniques has led to the ability to handle the volume of data while providing a continuous real time monitor of the status of a process.
In U.S. Pat. No. 5,483,468 (Chen et al.) is described a system and method for concurrently recording and displaying system performance data for a computing system. In this invention is described a method in which a user interacts with the data being displayed to create various analysis of that data with the intentions of improving the computer system performance.
Referring to U.S. Pat. No. 5,479,340 (Fox et al.) is described a multivariate analysis of components of an ongoing semiconductor process for real time in-situ control. In this invention the algorithm calculates the T.sup.2 value from Holding's T.sup.2 statistical analysis which in turn creates a feedback signal if the T.sup.2 value is out of range and stopping the process.
In U.S. Pat. No. 5,440,478 (Fisher et al.) a method and system for controlling a manufacturing process using statistical indicators of performance from the production process and specification data. The data is enter into a computer and displayed in tables and bar graphs to enable the production control manager to see unfavorable trends and processes out of control to allow adjustment of the manufacturing process before the process run is completed. Whereas U.S. Pat. No. 5,440,478 appears to have similarity to the invention described herein, it relies on manual collection and entry of data into a computing system for analysis and display.
A major problem with real time process control using real time data can be the volume of data that is produced by a process machine. This requires a system be established that can handle the volume of data without overwhelming the resulting process. It is important that old data to be available for long term trends analysis as well as for trouble shooting the process. Thus a system is needed that provides real time collection and analysis of the process data and allows the archiving of data no longer needed for real time analysis.